In a 3-1/2- or 4-quart slow cooker, place frozen green beans, cauliflower, undrained tomatoes, onion, celery, barley, garlic, and pepper. In a medium bowl, combine chicken broth and vegetable juice. Pour over vegetable mixture in cooker.
Cover and cook on low-heat setting for 6 to 8 hours or on high-heat setting for 3 to 4 hours. If desired, top each serving with pesto and Parmesean cheese. Makes 6 to 8 side-dish servings.